[PATCH] D56554: [ELF] Add '-z nognustack' opt to suppress emitting PT_GNU_STACK

[Rui Ueyama via Phabricator via cfe-commits]

ruiu added a comment.

In D56554#1353572 <https://reviews.llvm.org/D56554#1353572>, @krytarowski wrote:

> What do you think about this new logic:
>
> 1. specified `-z execstack` -> do not emit GNU STACK segment
> 2. specified `-z noexecstack` -> emit GNU STACK segment
> 3. no option specified -> detect `findSection(".note.GNU-stack")` (I might miss offhand some details here to be sure if it is reliable) 3.1. detected -> emit GNU STACK segment 3.2. not detected -> do not emit GNU STACK segment
>
>   Additionally we will specify explicitly in the clang driver for Linux and FreeBSD `-z noexecstack`.


I think I don't like the very idea of using "marker sections" in input object files to change the linker behavior. That's too subtle and seems error-prone to me.

After thinking for a while, I started thinking that the first version of this patch is probably exactly what we want. I had been thinking that `-z {no,}execstack` and `-z {no,}gnustack` are four different options, but what we actually want to get is tri-state:

- emit PT_GNU_STACK with RWX permission
- emit PT_GNU_STACK with RW permission
- do not emit PT_GNU_STACK

So we could map them to `-z {execstack,noexecstack,nognustack}`, respectively, with default set to `-z noexecstack`. You guys can pass `-z nognustack` to the linker to tell the linker to not emit it at all. That's exactly this patch does.


Repository:
  rLLD LLVM Linker

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https://reviews.llvm.org/D56554